During a heart attack, blood flow to the heart is interrupted, starving the tissue of oxygen (ischemia) and damaging or killing the heart muscle cells, the cardiomyocytes. This damaged or dying tissue (the infarction) fails to properly contract and pump blood, leaving heart attack survivors with lasting cardiac failure.

Currently, there is no way to replace or renew damaged heart tissue, but recent progress in regenerative medicine using stem cell therapy is showing promise in healing these “broken” hearts.

“In regenerative medicine, we try to restore some of this lost tissue in order to save lives as well as improve the quality of life,” says Antonis Hatzopoulos, Ph.D., associate professor of Medicine and Cell & Developmental Biology at Vanderbilt University Medical Center.

Only during early embryogenesis does our innate regenerative power rival that of worms and salamanders. As development progresses, the developmental trajectories of embryonic cells become more and more restricted, limiting the regenerative abilities of most human tissues. By adulthood, only a few tissues—skin, blood and the inner lining of the gut—regenerate easily, while in most tissues, regeneration is probably very restricted or nonexistent.

Regenerative capacity is conferred by either resident populations of stem cells that can give rise to new tissue cells when needed (for example, in skin and blood), adult cells that retain the ability to divide and grow (as in the liver), or a combination of the two.

“When it comes to cardiac regeneration, it looks like the heart has none of these mechanisms,” says Hatzopoulos, who has studied the regenerative capacity of the vasculature for more than a decade.

While recent studies have indicated that the heart may have a very small reserve of stem cells, they have yet to be identified and isolated, he says, so “scientists have turned to other sources of stem cells to see if they would be able to repair damaged heart tissue.”

Bone marrow is an easily accessible and plentiful source of stem cells. The bone marrow produces several different types of stem cells including the hematopoietic stem cells, which produce the circulating blood cells; mesenchymal stem cells, which can differentiate into a variety of cell types; and endothelial progenitor cells, which repair damaged blood vessel walls.